The present invention relates to a video conference control apparatus, video conference control method, and video conference control system.
Conventionally in an MCU (MicroControl Unit) having a window synthesis function, image data from respective terminals are decoded, and the decoded data are reduced in accordance with the window division number. At the same time, synthesized image data obtained by window division and multiplexing is encoded again, and the encoded data is output as a synthesized window to the respective terminals.
FIG. 4 shows an example of a video conference control system having this window synthesis function. Note that FIG. 4 shows only image synthesis, and all the functions about an audio system are not illustrated.
A video conference control system 100 is constituted by n video conference terminals 200 and a video conference control apparatus 300 connected to the video conference terminals 200 via a network. The video conference control apparatus 300 synthesizes transmitted images from the video conference terminals 200 and distributes the synthesized image to the video conference terminals 200.
The video conference terminal 200 is a video conference terminal complying with, e.g., ITU (International Telecommunication Union)-T_H. 320. In this case, encoding/decoding complying with ITU-T_H. 261 is performed.
The video conference control apparatus 300 connected to the video conference terminals 200 via a network using n lines has a window synthesis function. An encoding circuit 350 and a decoding circuit 320 must also comply with ITU-T_H. 261. The following example is based on encoding/decoding complying with ITU-T_H. 261.
An image transmitted from each video conference terminal 200 is demultiplexed into image data, audio data, and other data by a multiplexing/demultiplexing circuit 310 of the video conference control apparatus 300.
The terminal image data demultiplexed by the multiplexing/demultiplexing circuit 310 is decoded by the decoding circuit 320. The decoded data is thinned to 1/N in the horizontal and vertical directions and reduced to 1/N of one frame in accordance with the window division number by a thinning circuit 330 on the basis of a thinning timing signal. The resultant data is output as divided image data to an image synthesizing circuit 340.
The image synthesizing circuit 340 selects divided window data selected by a display window selection signal from respective divided image data, synthesizes (multiplexes) N windows on the basis of a synthesis timing signal (multiplexing timing signal), and outputs the N windows as synthesized image data to the encoding circuit 350.
The encoding circuit 350 compresses and encodes the synthesized image data as one image frame, and distributes the synthesized window to each video conference terminal 200 via the multiplexing/demultiplexing circuit 310. At the same time, the encoding circuit 350 outputs a compression/encoding frame timing signal to a window synthesis timing generating circuit 360.
The window synthesis timing generating circuit 360 outputs the frame timing signal, the thinning timing signal corresponding to a set window division number N, and the synthesis timing signal.
A video conference control apparatus having almost the same arrangement as that of the video conference control apparatus 300 is disclosed in Japanese Patent Laid-Open No. 2-5690.
In the conventional video conference control apparatus 300, the image quality may visually degrade near the boundary between divided windows.
FIG. 5 shows a display window when divided image data corresponding to the respective video conference terminals 200 are synthesized and displayed by the image synthesizing circuit 340.
In FIG. 5, one effective frame area represents an image data area actually encoded by the encoding circuit 350. This area is a unit for controlling encoding characteristics (e.g., quantization characteristics) in accordance with the information generation amount of an image in 352 pixels.times.288 lines in compliance with ITU-T_H. 261, and corresponds to a macroblock (16 pixels.times.16 lines: FCIF format) in compliance with ITU-T_H. 261. Note that FIG. 5 exemplifies a display window for the set window division number N=16.
In this case, since divided window areas are simply set in accordance with the window division number N=16, an area where the boundary between divided window areas does not always coincide with the boundary between encoding control blocks exists.
Near such a boundary between divided windows, e.g., a divided window having a large change in motion and coarse quantization characteristics and a divided window having a small change in motion and fine quantization characteristics are processed as the same encoding control block. For this reason, the image quality of the divided window having a small change in motion and fine quantization characteristics greatly degrades.
Also in the video conference control apparatus disclosed in Japanese Patent Laid-Open No. 2-5690, the image quality may visually degrade near the boundary between divided windows.